Display apparatus and method of manufacturing the same

ABSTRACT

A display apparatus includes a substrate, a first thin film transistor on the substrate, the first thin film transistor including an active layer including a source region, a drain region, and a channel region between the source region and the drain region, and a display device on the substrate and electrically connected to the first thin film transistor. The source region, the drain region, and the channel region include a first dopant and a second dopant, the second dopant being different from the first dopant. A concentration of the first dopant in the channel region is less than a concentration of the first dopant in the source region and the drain region.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This is a divisional application of U.S. patent application Ser. No.16/535,336, filed Aug. 8, 2019 (now U.S. Pat. No. 11,024,689), thedisclosure of which is incorporated herein by reference in its entirety.U.S. patent application Ser. No. 16/535,336 claims priority to andbenefit of Korean Patent Application No. 10-2018-0132563 under 35 U.S.C.§ 119, filed on Oct. 31, 2018, in the Korean Intellectual PropertyOffice, the entire contents of which are incorporated herein byreference.

BACKGROUND 1. Field

One or more embodiments relate to a display apparatus and a method ofmanufacturing the display apparatus. and more particularly, to a displayapparatus capable of improving image quality by improving deviceproperties and a method of manufacturing the display apparatus.

2. Description of the Related Art

As a display field for visually expressing various electrical signalinformation has rapidly developed, various flat panel displayapparatuses having excellent characteristics such as a small thickness,light weight, and low power consumption, etc. have been researched anddeveloped. An organic light-emitting display apparatus that is aself-emissive display apparatus does not need an additional lightsource, and thus, may be operated with a low voltage and may have alight weight and small thickness. In addition, the organiclight-emitting display apparatus is being highlighted as a nextgeneration display apparatus due to its excellent characteristics suchas wide viewing angles, high contrast, fast response speeds, etc.

An organic light-emitting display apparatus includes a plurality ofpixels. Pixels of an organic light-emitting display apparatus operatingin an analog driving method adjust brightness thereof according to amagnitude of input voltage or current data to express gray levels, andpixels of an organic light-emitting display apparatus operating in adigital driving method emit light of the same brightness but havedifferent emission time periods to express gray levels.

A display apparatus includes a thin film transistor and a capacitor anddrives a plurality of pixels by using the above devices and controlslight emission of the pixels.

SUMMARY

Embodiments are directed to a display apparatus including a substrate, afirst thin film transistor on the substrate, the first thin filmtransistor including an active layer including a source region, a drainregion, and a channel region between the source region and the drainregion, and a display device on the substrate and electrically connectedto the first thin film transistor. The source region, the drain region,and the channel region include a first dopant and a second dopant, thesecond dopant being different from the first dopant. A concentration ofthe first dopant in the channel region is less than a concentration ofthe first dopant in the source region and the drain region.

The first dopant may be a p-type dopant.

The second dopant may be inert gas ions.

A concentration of the second dopant may be uniform in the sourceregion, the drain region, and the channel region.

The first thin film transistor may further include a gate electrode, asource electrode, and a drain electrode, the source electrode and thedrain electrode respectively being connected to the source region andthe drain region. The display device may include a first electrodeelectrically connected to one of the source electrode and the drainelectrode, and a second electrode facing the first electrode.

The display device may further include an intermediate layer between thefirst electrode and the second electrode, the intermediate layerincluding an emission layer.

The active layer of the first thin film transistor may includepolycrystalline silicon. The display apparatus may further include asecond thin film transistor including an oxide semiconductor.

The substrate may be a flexible substrate.

Embodiments are also directed to a method of manufacturing a displayapparatus, the method comprising forming a thin film transistor on asubstrate, the thin film transistor including an active layer includinga source region, a drain region, and a channel region between the sourceregion and the drain region, and forming a display device electricallyconnected to the thin film transistor. Forming the thin film transistormay include forming an amorphous silicon layer on the substrate, dopingthe amorphous silicon layer with a first dopant and a second dopant, thesecond dopant being different from the first dopant, crystallizing theamorphous silicon layer, and forming the active layer by patterning thesilicon layer that is crystallized.

Forming the thin film transistor may further include forming a gateelectrode on the active layer, forming the source region, the drainregion, and the channel region on the active layer by doping the activelayer with the first dopant by using the gate electrode as a mask, andforming a source electrode and a drain electrode that are respectivelyconnected to the source region and the drain region. Forming the displaydevice may include forming a first electrode that is electricallyconnected to one of the source electrode and the drain electrode andforming a second electrode facing the first electrode.

Forming the display device may further include forming an intermediatelayer between the first electrode and the second electrode, theintermediate layer including an emission layer.

The first dopant and the second dopant may be dispersed in the amorphoussilicon layer simultaneously with crystallizing the amorphous siliconlayer.

Crystallizing the amorphous silicon layer may be at a temperature ofabout 350° C. to about 450° C.

The first dopant may be a p-type dopant.

The second dopant may be inert gas ions.

Doping the second dopant may be performed after doping the first dopant.

A mass of the second dopant may be greater than a mass of the firstdopant.

The amorphous silicon layer may be completely doped with the firstdopant and the second dopant before crystallizing the amorphous siliconlayer.

BRIEF DESCRIPTION OF THE DRAWINGS

Features will become apparent to those of skill in the art by describingin detail exemplary embodiments with reference to the attached drawingsin which:

FIG. 1 illustrates a plan view of a display apparatus according to anembodiment;

FIG. 2 illustrates an equivalent circuit diagram of one pixel in adisplay apparatus according to an embodiment;

FIGS. 3A to 3I illustrate cross-sectional views taken along line I-I′ ofFIG. 1 , illustrating stages of a process of manufacturing the displayapparatus of FIG. 1 ; and

FIGS. 4 and 5 illustrate graphs showing improvement in devicecharacteristics of a display apparatus according to an embodiment.

DETAILED DESCRIPTION

Example embodiments will now be described more fully hereinafter withreference to the accompanying drawings; however, they may be embodied indifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey exemplary implementations to those skilled in the art.

In the drawing figures, the dimensions of layers and regions may beexaggerated for clarity of illustration. It will also be understood thatwhen a layer or element is referred to as being “on” another layer orsubstrate, it can be directly on the other layer or substrate, orintervening layers may also be present. Further, it will be understoodthat when a layer is referred to as being “under” another layer, it canbe directly under, and one or more intervening layers may also bepresent. In addition, it will also be understood that when a layer isreferred to as being “between” two layers, it can be the only layerbetween the two layers, or one or more intervening layers may also bepresent. Like reference numerals refer to like elements throughout.

As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items. Expressions such as “atleast one of,” when preceding a list of elements, modify the entire listof elements and do not modify the individual elements of the list.

It will be understood that although the terms “first” and “second” areused herein to describe various elements, these elements should not belimited by these terms. Terms are only used to distinguish one elementfrom other elements.

The x-axis, the y-axis and the z-axis are not limited to three axes ofthe rectangular coordinate system, and may be interpreted in a broadersense. For example, the x-axis, the y-axis, and the z-axis may beperpendicular to one another, or may represent different directions thatare not perpendicular to one another.

FIG. 1 illustrates a plan view of a display apparatus 10 according to anembodiment, and FIG. 2 illustrates an equivalent circuit diagram of onepixel in the display apparatus 10 according to the embodiment.

Referring to FIG. 1 , the display apparatus 10 according to anembodiment includes a display area DA on which an image is displayed anda peripheral area PA outside the display area DA. The substrate 100includes the display area DA and the peripheral area PA.

A plurality of pixels P are located in the display area DA. FIG. 2illustrates an equivalent circuit diagram of one pixel P. Referring toFIG. 2 , a pixel P may include a pixel circuit PC connected to a scanline SL and a data line DL and a display device connected to the pixelcircuit PC. The display device may include, for example, an organiclight-emitting diode OLED.

The pixel circuit PC may include a driving thin film transistor Td, aswitching thin film transistor Ts, and a storage capacitor Cst. Theswitching thin film transistor Ts may be connected to the scan line SLand the data line DL and may transfer a data signal input through thedata line DL to the driving thin film transistor Td according to a scansignal input through the scan line SL. The storage capacitor Cst may beconnected to the switching thin film transistor Ts and a driving voltagesupply line PL and may store a voltage corresponding to a differencebetween a voltage transferred from the switching thin film transistor Tsand a driving voltage ELVDD supplied to the driving voltage supply linePL.

The driving thin film transistor Td may be connected to the drivingvoltage supply line PL and the storage capacitor Cst and may control adriving current flowing from the driving voltage supply line PL to theorganic light-emitting diode OLED in response to the voltage valuestored in the storage capacitor Cst. The organic light-emitting diodeOLED may emit light having a predetermined luminance according to thedriving current. The organic light-emitting diode OLED may emit, forexample, red light, green light, blue light, or white light.

The pixel circuit PC of the pixel P may be variously modified. FIG. 2shows an example in which the pixel P includes two thin film transistorsand one storage capacitor. In some implementations, the pixel circuit PCof the pixel P may include, for example, three or more thin filmtransistors or two or more storage capacitors.

The peripheral area PA includes a pad area PADA to which variouselectronic devices, a printed circuit board, etc. are electricallyattached. A first voltage line 70 and a second voltage line 80 supplyingelectric power for driving the display device may be located on theperipheral area PA. The first voltage line 70 may be a common voltageELVSS line, and the second voltage line 80 may be a driving voltageELVDD line. The first voltage line 70 may be connected to a commonelectrode 220 directly or via another wiring, and the second voltageline 80 may be connected to the driving voltage supply line PL.

In addition, FIG. 1 may be appreciated as a plan view showing thesubstrate 100 of FIG. 3I during manufacturing processes of the displayapparatus 10. In a final product of the display apparatus 10 or anelectronic device such as a smartphone including the display apparatus10, the substrate 100 may be partially bent in order to reduce an areaof the peripheral area PA visible in a plan view by a user. For example,the substrate 100 may be bent between the pad area PADA and the displayarea DA, and thus, the pad area PADA may at least partially overlap thedisplay area DA. The bending direction may be set so that the pad areaPADA is located behind the display area DA, for example, so that the padarea PADA does not cover the display area DA. Accordingly, the user mayrecognize that the display area DA in a plan view occupies most of thedisplay apparatus 10.

Hereinafter, a structure of the pixel P and processes of manufacturingthe pixel P will be described in detail with reference to FIGS. 3A to3I.

FIGS. 3A to 3I illustrate cross-sectional views taken along line I-I′ ofFIG. 1 , depicting stages of a process of manufacturing the displayapparatus 10 of FIG. 1 .

As shown in FIG. 3A, the substrate 100 may be prepared, and an amorphoussilicon layer 110 a may be formed on the substrate 100.

The substrate 100 may include various materials, for example, a glassmaterial, a metal material, a plastic material such as polyethyleneterephthalate (PET), polyethylene naphthalate (PEN), polyimide, etc.

As an embodiment, the substrate 100 may include a flexible substrate.For example, the substrate 100 may include polyimide (PI). When theflexible substrate is used, the display apparatus 10 according to theembodiment may be a flexible display apparatus.

The amorphous silicon layer 110 a may be formed by depositing amorphoussilicon on the substrate 100 by a plasma-enhanced chemical vapordeposition (PECVD) method or a low pressure CVD (LPCVD) method. A bufferlayer 101 may be formed on the substrate 100 prior to forming theamorphous silicon layer 110 a.

The buffer layer 101 may block impurities or moisture that may try toinfiltrate through the substrate 100. The buffer layer 101 may include,for example, an inorganic material, such as silicon oxide (SiOx),silicon nitride (SiNx), and/or silicon oxynitride (SiON), and may have asingle-layered or multi-layered structure. The buffer layer 101 maycorrespond to the display area DA and the peripheral area PA and may beobtained by depositing the above-described inorganic material on thesubstrate 100 by a CVD or atomic layer deposition (ALD) method.

As shown in FIG. 3B, the amorphous silicon layer 110 a may be doped witha first dopant D1.

The amorphous silicon layer 110 a may be doped by first dopant D1 by asuitable method, for example, by an ion implantation method. When theion implantation method is used, the first dopant D1 in an ionized statemay be accelerated to tens to hundreds KeV and implanted into theamorphous silicon layer 110 a. The first dopant D1 may be doped in aconcentration of 1.3×10¹² to 1×10¹³ per 1 cm³.

The first dopant D1 may be a p-type dopant or an n-type dopant. Thep-type dopant may be, for example boron (B), aluminum (Al), gallium(Ga), or indium (In). The n-type dopant may be, for example phosphorus(P), arsenic (As), antimony (Sb), or bismuth (Bi).

In an embodiment, the first dopant D1 may be a p-type dopant. A case inwhich the first dopant D1 includes boron (B) as one of the p-typedopants will be described below.

As shown in FIG. 3C, the amorphous silicon layer 110 a may be doped witha second dopant D2. For example, the amorphous silicon layer 110 a thatis already doped with the first dopant D1 may then be doped with thesecond dopant D2.

As described with respect to the first dopant D1, the ion implantationmethod may also be used for doping the amorphous silicon layer 110 awith the second dopant D2 by. The second dopant D2 may be doped in aconcentration of 1×10¹³ per 1 cm³.

The second dopant D2 may be different from the first dopant D1. Forexample, the second dopant D2 may include an inert gas ion. A mass ofthe second dopant D2 may be greater than that of the first dopant D1.For example, the inert gas may be selected from helium (He), neon (Ne),argon (Ar), krypton (Kr), and xenon (Xe).

As described above, when the inert gas ion is used as the second dopantD2, influence on the device may be reduced and an undesirable chemicalreaction on films of the amorphous silicon layer 110 a or the bufferlayer 101 during the processes may be avoided.

When an inert gas ion having greater mass than that of Xe is used as thesecond dopant D2, the ion implantation may not be sufficientlyperformed. Moreover, even when the implantation is performed, theamorphous silicon layer 110 a may be damaged. Thus, the second dopant D2may include a material having a mass less than that of Xe.

As an embodiment, the second dopant D2 may include Ar ions. Hereinafter,a case in which the second dopant D2 includes Ar positive ions (Ar+)will be described below.

The process of doping the first dopant D1 shown in FIG. 3B and theprocess of doping the second dopant D2 shown in FIG. 3C may be performedbefore crystallization of the amorphous silicon layer 110 a. Theamorphous silicon layer 110 a may be completely doped with the firstdopant D1 and the second dopant D2.

As described above, when the first dopant D1 is entirely implanted intothe amorphous silicon layer 110 a, the dopant may be included in achannel region, as well as in a source region and a drain region of anactive layer in a thin film transistor. Thus, it may be easy to controla threshold voltage Vth of the thin film transistor.

The second dopant D2 that does not generate chemical transformation ofthe amorphous silicon layer 110 a may be additionally implanted.Accordingly, device characteristics such as hysteresis of the thin filmtransistor may be improved. The second dopant D2 may affect theamorphous silicon layer 110 a while being ion-implanted and crystalseeds may be reduced. Crystals having defective ability to crystallizemaybe reduced and crystals having excellent ability to crystallize mayincrease. Fine grains that generate at a relatively low temperature maybe broken due to the action of the second dopant D2 while a temperatureto crystallize the amorphous silicon layer 110 a may be increased.Accordingly, defective crystals may be reduced.

The order of the first dopant D1 doping process and the second dopant D2doping process may be changed. However, the second dopant D2 having agreater mass than the first dopant D1 is likely to be distributedrelatively under the first dopant D1 (e.g., −Z direction), when thesecond dopant D2 is implanted earlier than the first dopant D1. Thesecond dopant D2 may sink at a bottom side of the amorphous siliconlayer 110 a and much time and energy may be necessary to activate thesecond dopant D2 at a later time. Therefore, in some implementations,the second dopant D2 may be implanted later than the first dopant D1 sothat the second dopant D2 may be distributed above the first dopant D1.The first and second dopants D1 and D2 may be easily activated andprovided uniformly.

As shown in FIG. 3D, the amorphous silicon layer 110 a doped with thefirst dopant D1 and the second dopant D2 may be crystallized.

For example, a laser beam L may be irradiated onto the amorphous siliconlayer 110 a to increase a temperature of the amorphous silicon layer 110a to a desired temperature. The amorphous silicon layer 110 a may betransformed into a polycrystalline silicon layer. A source of the laserbeam L may be excimer laser.

When the substrate 100 is a flexible substrate including polyimide (PI),a crystallization temperature may be about 350° C. to about 450° C. Ifthe crystallization were to be performed at a temperature equal to orhigher than 450° C., PI, that is, the material included in thesubstrate, could be damaged. On the other hand, when the crystallizationtemperature is lower than 350° C., it may be difficult to sufficientlycrystallize the amorphous silicon layer 110 a.

While the amorphous silicon layer 110 a is crystallized, the firstdopant D1 and the second dopant D2 may be activated. The temperature ofthe amorphous silicon layer 110 a may increase while the amorphoussilicon layer 110 a is crystallized. Accordingly, the first dopant D1and the second dopant D2 implanted in the amorphous silicon layer 110 abefore the crystallization may be dispersed in the amorphous siliconlayer 110 a simultaneously with the crystallization of the amorphoussilicon layer 110 a. The first and second dopants D1 and D2 may beevenly distributed in the amorphous silicon layer 110 a without the needto perform an additional thermal treatment for diffusing the first andsecond dopants D1 and D2. Thus, the polycrystalline silicon layer mayhave an even doping concentration.

A result corresponding to that of the thermal treatment of the first andsecond dopants D1 and D2 may be obtained by only crystallizing theamorphous silicon layer 110 a without performing an additional thermaltreatment. Thus, a processing time and manufacturing costs may bereduced.

Next, as shown in FIG. 3E, the silicon layer crystallized to apolycrystalline silicon layer may be patterned to form an active layer110.

The silicon layer may be patterned in various ways, for example, by adry etching method or a wet etching method using photoresist.

As described above, the active layer 110 may include polycrystallinesilicon. In some implementations, the thin film transistors may includean active layer having a material other than polycrystalline silicon.

As an embodiment, the driving thin film transistor Td shown in FIG. 2may include an active layer including polycrystalline silicon. In someimplementations, the switching thin film transistor Ts (see FIG. 2 ) mayinclude an active layer including an oxide semiconductor. The oxidesemiconductor may include a metal oxide such as oxides of zinc (Zn), In,Ga, tin (Sn), titanium (Ti), etc., or a mixture of metal such as Zn, In,Ga, Sn, Ti, etc. For example, the oxide semiconductor may include Znoxide-based material, e.g., Zn oxide, In—Zn oxide, Ga—In—Zn oxide, etc.In some embodiments, the oxide semiconductor may include an IGZO(In—Ga—Zn—O) semiconductor including metal such as In or Ga in ZnO. Insome implementations, the active layer of the switching thin filmtransistor Ts (see FIG. 2 ) may include an oxide semiconductor, and theactive layer of the driving thin film transistor Td (see FIG. 2 ) mayinclude polycrystalline silicon.

When the active layer of the thin film transistor includes the oxidesemiconductor, a low off-current may be exhibited and low-frequencydriving may be implemented. When one of the driving and switching thinfilm transistors Td and Ts includes an oxide semiconductor layer, powerconsumption of the display apparatus 10 (see FIG. 1 ) may be reduced.

As shown in FIG. 3F, a gate insulating layer 102 may be formed to coverthe active layer 110, and a gate electrode 120 may be formed on the gateinsulating layer 102.

The gate insulating layer 102 may insulate the active layer 110 and thegate electrode 120 from each other. To this end, the gate insulatinglayer 102 may include an insulating layer obtained by depositing aninorganic material such as SiON, SiOx, and/or SiNx by a CVD or ALDmethod. The above insulating layer including the inorganic material mayhave a single-layered or multi-layered structure.

The gate electrode 120 may be obtained by patterning a conductive metalthat is deposited by a sputtering method or a vacuum evaporation method.The gate electrode 120 may at least partially overlap the active layer110.

As shown in FIG. 3F, the active layer 110 under the gate electrode 120may be doped with the first dopant D1 by using the gate electrode 120 asa mask.

The first dopant D1 may not be implanted to a portion of the activelayer 110 that overlaps the gate electrode 120, but instead may beimplanted into a remaining region of the active layer 110. As such, theactive layer 110 may be partitioned into a source region 110 s, a drainregion 110 d, and a channel region 110 c between the source and drainregions 110 s and 110 d. The source region 110 s and the drain region110 d may be respectively connected to a source electrode and a drainelectrode to be described below.

The first dopant D1 additionally doped in this process may be added tothe first dopant D1 previously doped (see FIG. 3B). The concentration ofthe first dopant D1 in the source region 110 s and the drain region 110d of the active layer 110 may increase. As such, the concentration ofthe first dopant D1 in the channel region 110 c may be lower than thatin the source region 110 s and the drain region 110 d.I In order toprovide a difference between concentrations of the source and drainregions 110 s and 110 d and the channel region 110 c clear, the firstdopant D1 may be doped in a concentration of 1.3×10¹⁵ per 1 cm³.

The second dopant D2 may not be additionally doped. Accordingly, thesecond dopant D2 may have a uniform concentration throughout the sourceregion 110 s, the drain region 110 d, and the channel region 110 c.

As shown in FIG. 3H, after forming an interlayer insulating layer 103 tocover the gate electrode 120, a source electrode 130 s and a drainelectrode 130 d may be formed on the interlayer insulating layer 103.

The interlayer insulating layer 103 may be obtained by depositing aninorganic material such as SiON, SiOx, and/or SiNx by a CVD or ALDmethod. The interlayer insulating layer 103 may have a single-layered ormulti-layered structure.

Before forming the source electrode 130 s and the drain electrode 130 don the interlayer insulating layer 103, a through hole may be providedin the gate insulating layer 102 and the interlayer insulating layer103. The source region 110 s and the drain region 110 d of the activelayer 110 may be partially exposed through the through hole.

A conductive metal may be deposited on the interlayer insulating layer103 by a sputtering method or a vacuum deposition method. The conductivemetal may be patterned by using a mask, and the source electrode 130 sand the drain electrode 130 d electrically connected to the sourceregion 110 s and the drain region 110 d via the through hole may beobtained.

As shown in FIG. 3I, a first thin film transistor T1 including theactive layer 110, the gate electrode 120, the source electrode 130 s,and the drain electrode 130 d is obtained.

As shown in FIG. 3I, a planarization layer 104 may be formed on thefirst thin film transistor T1. The planarization layer 104 may include ageneral universal polymer (polymethylmethacrylate (PMMA) or polystyrene(PS)), a polymer derivative having phenol groups, an acryl-basedpolymer, an imide-based polymer, an aryl ether-based polymer, anamide-based polymer, a fluoride-based polymer, a p-xylene-based polymer,a vinyl alcohol-based polymer, or a blend thereof. As an embodiment, theplanarization layer 104 may include PI. The planarization layer 104 maybe formed using a vacuum deposition method.

A display device may be formed on the planarization layer 104. As anembodiment, the display device may include an organic light-emittingdiode 200. Hereinafter, a case in which the display device is theorganic light-emitting diode 200 will be described below.

The organic light-emitting diode 200 may include a pixel electrode 210,a common electrode 220, and an intermediate layer 215 including anemission layer between the pixel electrode 210 and the common electrode220.

The pixel electrode 210 may contact one of the source electrode 130 sand the drain electrode 130 d via an opening 210 h provided in theplanarization layer 104 to be electrically connected to the first thinfilm transistor T1. As such, the first thin film transistor T1 mayfunction as the driving thin film transistor Td (see FIG. 2 ). Althoughnot shown in FIG. 3I, the switching thin film transistor Ts (see FIG. 2) may be further provided in addition to the first thin film transistorT1.

A pixel defining layer 105 may be formed on the pixel electrode 210. Thepixel defining layer 105 may have an opening corresponding to a pixel P(see FIG. 2 ), for example, an opening exposing at least a centerportion of the pixel electrode 210 to define a light-emission region.The pixel defining layer 105 may increase a distance between an edge ofthe pixel electrode 210 and the common electrode 220, to prevent thegeneration of an arc between the pixel electrode 210 and the commonelectrode 230. The pixel defining layer 105 may include an organicmaterial, for example, polyimide, hexamethyl disiloxane (HMDSO), etc.

The intermediate layer 215 may include a low-molecular weight organicmaterial or a polymer material. When the intermediate layer 215 includesa low-molecular weight material, the intermediate layer 215 may includea hole injection layer (HIL), a hole transport layer (HTL), an emissionlayer (EML), an electron transport layer (ETL), and an electroninjection layer (EIL) in a single or multiple-layered structure.Examples of the low-molecular weight material may include copperphthalocyanine (CuPc), N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidine(NPB), and tris-8-hydroxyquinoline aluminum (Alq₃). The above layers maybe formed using a screen printing method, an inkjet printing method, alaser induced thermal imaging (LITI) method, etc.

When the intermediate layer 215 includes a polymer material, theintermediate layer 215 may include an HTL and an EML. Here, the HTL mayinclude poly(3,4-ethylenedioxythiophene) PEDOT, and the EML may includea poly-phenylenevinylene (PPV)-based or polyfluorene-based polymermaterial. The intermediate layer 215 may have various structures. Forexample, the intermediate layer 215 may include at least one layer thatis integrally formed throughout a plurality of pixel electrodes 210. Insome implementations, the intermediate layer 215 may include a layerthat is patterned to correspond to each of the plurality of pixelelectrodes 210.

The common electrode 220 may be formed above the display area DA and maycover the display area DA. The common electrode 220 may be integrallyprovided with respect to a plurality of pixels P (see FIG. 2 ).

An encapsulation layer may be provided to cover the organiclight-emitting diode 200 in order to protect the organic light-emittingdiode 200 against external moisture or oxygen. The encapsulation layermay include an inorganic encapsulation layer and an organicencapsulation layer. The inorganic and organic encapsulation layers maybe stacked alternately with each other.

The display apparatus 10 (see FIG. 1 ) manufactured as above may improvevarious device characteristics, as described in detail below withreference to FIGS. 4 and 5 .

FIGS. 4 and 5 are graphs showing improvement in device characteristicsof a display apparatus according to an embodiment.

In the graphs of FIGS. 4 and 5 , the transverse axis denotes threesamples and the longitudinal axis denotes a measured value of devicecharacteristics.

The three samples include a reference sample S0, a first sample S1, anda second sample S2. The reference sample S0 is a display apparatus inwhich the amorphous silicon layer is only doped with B (corresponding tothe first dopant D1 described above) at a concentration of B is 1.3×10¹²per 1 cm³.

The first sample S1 is a display apparatus according to an embodiment,in which the amorphous silicon layer is doped with both B and Ar ions(corresponding to the second dopant D2 described above), and the dopingprocess is performed before the crystallization of the amorphous siliconlayer. In the first sample S1, a doping concentration of B is 1.3×10¹²per 1 cm³, and a doping concentration of Ar ions is 1×10¹³ per 1 cm³.

The second sample S2 is a display apparatus according to a comparativeexample, in which the amorphous silicon layer is doped with both B andAr ions, and the doping process is performed after the crystallizationof the amorphous silicon layer. Like in the first sample S1, in thesecond sample S2, a doping concentration of B is 1.3×10¹² per 1 cm³ anda doping concentration of Ar ions is 1×10¹³ per 1 cm³.

Referring to FIG. 4 , according to the reference sample S1, a medianvalue of a threshold voltage Vth is −3.41, and according to the firstsample S1, a median value of a threshold value Vth is −3.23. On theother hand, according to the second sample S2, even though the Ar ionsare doped in addition to B, the median value of the threshold value Vthis reduced to −8.57.

Next, referring to FIG. 5 , in the reference sample S0, a median valueof hysteresis (delta Vth), which is defined as a variation in thethreshold voltage Vth, is 0.243. In the first sample S1, a median valueof the hysteresis (delta Vth) is −3.23. However, in the second sampleS2, a median value of the hysteresis (delta Vth) was 0.379 even when Arions were doped in addition to B.

Therefore, when B and Ar are all doped before the crystallizationprocess as in the one or more embodiments, the threshold voltage Vth maybe reduced and the hysteresis (delta Vth) may be decreased as comparedwith a case in which B is only doped. As shown in FIG. 5 , the displayapparatus according to the embodiment (corresponding to the first sampleS1) may have the hysteresis (delta Vth) that is improved by 15.1% ascompared with the display apparatus (corresponding to the referencesample S0) in which B is only doped and Ar ions are not doped.

On the other hand, in the comparative example (corresponding to thesecond sample S2) in which B and Ar ions are doped after thecrystallization process, the threshold voltage Vth and the hysteresis(delta Vth) both are increased greatly as compared with the displayapparatus (reference sample S0).

By way of summation and review, electrical and physical characteristicsof a display apparatus are highly relevant with respect to image qualityof the display apparatus. One of the significant issues in the field ofdisplays is to improve device characteristics.

Embodiments provide a display apparatus capable of improving imagequality by improving device properties and a method of manufacturing thedisplay apparatus.

As described above, according to the display apparatus of theembodiment, the image quality of the display apparatus may be improvedby improving characteristics of the devices, and in particular, theafterimage effect may be reduced by decreasing the hysteresis. Accordingto the method of manufacturing the display apparatus of the embodiment,the influence of the improvement in the device characteristic on anotherdevice characteristic may be reduced, and accordingly, processing timeand manufacturing costs may be reduced.

According to the embodiment, the image quality of the display apparatusmay be improved by improving characteristics of the devices.

Also, the occurrence of afterimage due to the hysteresis may be reduced.

In addition, the influence on another device characteristic during theimprovement of a certain device characteristic may be reduced.

In addition, processing time and manufacturing costs of the displayapparatus may be reduced.

Example embodiments have been disclosed herein, and although specificterms are employed, they are used and are to be interpreted in a genericand descriptive sense only and not for purpose of limitation. In someinstances, as would be apparent to one of ordinary skill in the art asof the filing of the present application, features, characteristics,and/or elements described in connection with a particular embodiment maybe used singly or in combination with features, characteristics, and/orelements described in connection with other embodiments unless otherwisespecifically indicated. Accordingly, it will be understood by those ofskill in the art that various changes in form and details may be madewithout departing from the spirit and scope thereof as set forth in thefollowing claims.

What is claimed is:
 1. A display apparatus, comprising: a substrate; afirst thin film transistor on the substrate, the first thin filmtransistor including an active layer including a source region, a drainregion, and a channel region between the source region and the drainregion; and a display device on the substrate and electrically connectedto the first thin film transistor, wherein the source region, the drainregion, and the channel region include a first dopant and a seconddopant, the second dopant being different from the first dopant, and aconcentration of the first dopant in the channel region is less than aconcentration of the first dopant in the source region and the drainregion.
 2. The display apparatus as claimed in claim 1, wherein thefirst dopant is a p-type dopant.
 3. The display apparatus as claimed inclaim 1, wherein the first type dopant is an n-type or p-type dopant,and the second dopant is inert gas ions.
 4. The display apparatus asclaimed in claim 1, wherein a concentration of the second dopant isuniform in the source region, the drain region, and the channel region.5. The display apparatus as claimed in claim 1, wherein: the first thinfilm transistor further includes a gate electrode, a source electrode,and a drain electrode, the source electrode and the drain electroderespectively being connected to the source region and the drain region,and the display device includes a first electrode electrically connectedto one of the source electrode and the drain electrode, and a secondelectrode facing the first electrode.
 6. The display apparatus asclaimed in claim 5, wherein the display device further includes anintermediate layer between the first electrode and the second electrode,the intermediate layer including an emission layer.
 7. The displayapparatus as claimed in claim 1, wherein: the active layer of the firstthin film transistor includes polycrystalline silicon, and the displayapparatus further includes a second thin film transistor including anoxide semiconductor.
 8. The display apparatus as claimed in claim 1,wherein the substrate is a flexible substrate.
 9. The display apparatusas claimed in claim 1, wherein a concentration of the second dopant isuniform in the source region, the drain region, and the channel region.10. The display apparatus as claimed in claim 3, wherein the inert gasions are one of helium (He), neon (Ne), argon (Ar), krypton (Kr) ions,or xenon (Xe) ions.
 11. The display apparatus as claimed in claim 10,wherein the inert gas ions are argon ions.
 12. The display apparatus asclaimed in claim 10, wherein a concentration of the inert gas ions isuniform in the source region, the drain region, and the channel region.13. The display apparatus as claimed in claim 10, wherein aconcentration of the inert gas ions is at least 1×10¹³ per 1 cm³.